1. Field of the Invention
The invention relates to a roll, comprised of a roll body having a central bore, wherein flanged necks are flange-mounted at both ends of the roll body for supporting the roll body in bearings.
2. Description of the Related Art
For manufacturing such-rolls liquid metal is poured into a casting die where the metal cools slowly. Because of the different cooling effects with the rolls across their cross-section, a chilled cast material having an inhomogeneous microstructure results. Moreover, the roll body during cooling will shrink and become detached from the walls of the casting die. Because of this, outer contours of the rolls can result that deviate from a cylindrical shape.
Subsequent to the cooling process, the roll body is mediated and ground to a cylindrical shape. Because of this, at certain locations the outer layer of the roll may be removed to a greater extent than at other locations so that a cylindrical body will result as a result of the grinding process but the inhomogeneous zones of the material of the roll may increase. When such a roll body is rotated, it exhibits imbalance because of the inhomogeneous mass distribution.
Because of the relatively high rotary speed, for example, in the case of paper calenders, dynamic bending of the rolls also occurs in addition to the error sources caused by the nonuniform mass distribution, and this dynamic bending represents an additional error source. Additional errors may result from bearing play; all these errors can be additive but they can also act in a compensating way.
When the roll is heated for operation, non-uniform thermal expansion of the roll body can cause additional bending of the roll and thus can cause additional errors that appear as an additional imbalance.
It is already known to insert a cage into the central bore of the rolls of the aforementioned kind; such a cage has several partitions. In these rolls, the imbalance is determined in the cold state, and appropriate counterweights are calculated with regard to their mass and their angles and introduced into the cage at appropriate partition positions. After insertion of the weights, the flanges are screwed on and a test run is started. If additional imbalance is measured, the flanges must be removed again and additional weights must be introduced into the cage so that subsequently the flanges must be screwed on again and the roll must again be subjected to a new test run.
Moreover, it is known to introduce two or several deep hole bores that are displaced relative to one another into the roll body wherein one or several of the bores are not completely drilled through in order to introduce a mass for eccentricity compensation. The reference circle can be selected as desired across the cross-section. It is advantageous to select the screw connection bores for receiving the screw connections of the roll neck; this has the advantage that the neck must not be removed. However, this method is greatly limiting with regard to the compensation mass.
In new multi-nip calender rolls, thermal transfer efficiencies, surface temperatures, and operating speeds are required that, in connection with the slim design of the rolls, pose special requirements on the smooth running qualities of the rolls. When imbalance results, in the case of open rolls the bearings and the entire stand can be loaded excessively. In the case of closed nips, more than proportional loads of the additional rolls that support the rolls are present so that their coatings are worn more quickly.